Method and apparatus for the cooling of an object

ABSTRACT

A method of and an apparatus for the cooling of an object, such as a superconductive magnet, superconductive cable system or the like, wherein the liquid cryogen (e.g. a liquified gas such as helium) is passed continuously through or in heat-exchanging relationship with the object from a supply reservoir. After traversing the object or a cryostat therefor, the liquid cryogen is partially expanded to form a gas/liquid phase mixture which is passed in heat-exchanging relationship with previously warmed and compressed coolant and is fully vaporized thereby. The vaporized cryogen is then used to pick up heat from the system, is compressed and is cooled by the aforementioned heat exchange before being expanded to bring about liquefaction with the liquid being collected in the reservoir.

United States Patent [I 1 Asztalos Apr. 22, 1975 METHOD AND APPARATUSFOR THE Primary Examiner-Meyer Perlin COOLING OF AN OBJECT AssistantE.\'aminerR0na1d C Capossela [75] Inventor: Stefan Asztalos, Munich,Germany Agent or Firm-Karl Ross; Herbert Assignee: LindeAkiengesellschaft,

Wiesbaden, Germany [22] Filed: Feb. 13., 1974 [21] Appl. No.: 441,955

[30] Foreign Application Priority Data Feb. 20. 1973 Germany 2308301[52] US. Cl. 62/62; 62/50; 62/467; 62/514 [51] Int. Cl. F2 5d 31/00 [58]Field of Search 62/45, 50-55, 62/467, 512. 514, 62, 64

[56] References Cited UNITED STATES PATENTS 3,159 008 12/1964 Nebgcn62/512 X 3,364,687 1/1968 Kolm 62/467 X 3.415.077 10/1968 Collins...62/467 3.611,740 10/1971 Gigcr .7 62/514 X R4014 new 3 [57] ABSTRACT Amethod of and an apparatus for the cooling of an object. such as asuperconductive magnet. superconductive cable system or the like whereinthe liquid cryogen (e.g. a liquified gas such as helium) is passedcontinuously through or in heat-exchanging relationship with the objectfrom a supply reservoir. After traversing the object or a cryostattherefor. the liquid cryogen is partially expanded to form a gas/liquidphase mixture which is passed in heat-exchanging relationship withpreviously warmed and compressed coolant and is fully vaporized thereby.The vaporized cryogen is then used to pick up heat from the system. iscompressed and is cooled by the aforementioned heat exchange beforebeing expanded to bring about liquefaction with the liquid beingcollected in the reservoir.

17 Claims, 1 Drawing Figure CROSS REFERENCE TO RELATED APPLICATION Thepresent Application is related to the commonly assigned copcndingapplication Ser. No. 435,856 filed Jan. 23, 1974 of myself and other andentitled METHOD OF AND APPARATUS FOR THE COOL- ING OF AN OBJECT FIELD OFTHE INVENTION My present invention relates to a method of and anapparatus for the cooling of an object such as a superconductive magnetor a superconductive cable in a housing or cryostat with a liquidcoolant or cryogen, e.g. liquid helium.

BACKGROUND OF THE INVENTION The deep cooling of objects has been foundto be especially advantageous in recent years for the cooling ofconductors in electrical systems, the conductivity of a conductorincreasing as its temperature is reduced in the great majority of cases.The development of superconductive materials has caused increasinginterest in cooling systems adapted to reach superconductivetemperatures, i.e. temperatures of I4K or below, and in the handling ofcryogenic liquids, i.e. liquefied gases capable of reaching these lowtemperatures.

Superconductors are used, for example, in magnets of particleaccelerators, spectrometers and other systerns in which high magneticfield strengths must be developed with limited cross-sections of theconductor.

Moreover, superconductors are used in cables for the transmission oflarge currents over both small and large distances.

A typical cryogen-liquid-cooled cable may comprise a plurality ofcoaxial ducts in which the superconductor is received in an inner ductand an outer space is evacuated and/or provided with so-calledsuperinsulation composed of alternating layers of filamentary materialand heat-reflective foil. The cryogen liquid or cryogen is caused toflow through the innermost duct in intimate (direct) contact orheat-exchanging relation with the conductor. Superconductor magnets areoften enclosed in highly insulated housings or cryostats to which theconductive liquid is admitted or are provided with channels, e.g. themagnet windings themselves, to which the cryogenic liquid is admitted.

it has been the practice prior to the system described in theaforementioned copcnding application, to supply liquid helium to theobject from a first storage vessel and to conduct the liquid after ithas traversed the object into a second storage vessel. A pressuredifferential, produced by some pressure-buildup means, is maintainedacross the vessel to obtain the driving pressure necessary to displacethe liquid from the first vessel through the object and into the secondvessel.

When the first vessel is emptied, the pressure differential is reversedand the liquid, now collected in the second vessel, is displaced in theopposite direction by an opposite pressure differential through thehousing and into the first vessel.

The disadvantage of that system is that the housing cannot be suppliedfor prolonged periods continuously with the cryogenic liquid from onevessel and hence there are periods in which the flow of the cryogen mustbe interrupted. This of course has the concomittant disadvantage thatuniform flow and cooling cannot be guaranteed and that even briefinterruptions in the con- I tinuity of coolant flow may causedetrimental results when the cooled object is a superconductive magnetor superconductive cable.

To overcome these disadvantages, the system described in theaforementioned copcnding application provides that the cryogenic liquidis collected after traversing the object from a first vessel and afterbeing expanded to transform it into a gas/liquid phase mixture which isseparated in the second or receiving vessel with the liquid phase beingtransferred to a third vessel and intermittently discharged by anappropriate pressure differential into the first vessel.

More particularly, the prior application discloses a method of coolingan object in a housing, especially a superconductive magnet or asuperconductive cable, which comprises feeding a cryogenic liquid from afirst or supply vessel to the object (e.g. a housing, duct, orcryostat), collecting the cryogenic liquid from the housing in a secondvessel, expanding the liquid in the second vessel to cool the liquid andproduce by partial vaporization thereof a vapor/phase mixed with aliquid/phase, separating the vapor phase from the liquid phase of thesecond vessel, feeding the liquid phase to a third vessel and at leastintermittently returning liquid from the third or storage vessel to thefirst or supply vessel. Thus that application provided for expansion ofthe liquid cryogen or coolant after it had been used to cool the object,thereby lowering the temperature of the liquid phase and abstractingheat therefrom equivalent to the latent heat of vaporization of thecryogen. Thereafter, a phase separation was carried out whereby theliquid component was collected in the third or storage vessel and wasthen resupplied to the first or supply vessel. That system had theadvantage that it was able to achieve cooling of an object, e.g. asuperconductive system, with a liquid coolant or cryogen, e.g. liquidhelium, with one-way, continuous and long duration (noninterrupted) flowof the cryogen from a single supply vessel to the object.

The liquid coolant was displaced through the system with appropriatedriving pressures and thus the pressure differential between the firstand second vessel was maintained at the level necessary to drive thecryogen from the first or supply vessel through the cryostathousing orobject and into the second or phaseseparation vessel. During theaccumulation of the liquid in the storage vessel the latter wasmaintained at the same pressure as the second vessel, i.e. at a pressurelower than that in the first vessel. Even the expansion step within thesecond vessel took place to a pressure below that in the first or supplyvessel.

While the system of the aforementioned copending application representsa major advance over the art of cryogenic cooling of objects, especiallysuperconductive systems, it has some characteristics which are notalways desirable. For example, the continuous cooling system requiredsubstantially periodic pressure buildup and pressure reduction in thethird or storage vessel and consequently heat losses are unavoidable,furthermore, the pressure control system necessary to provide theseperiodic pressure variations may be more complex than is desirable.

OBJECT OF THE INVENTION It is, therefore, an important object of thepresent invention to provide a method of and an apparatus for thecooling of a body, eg a superconductive system, with a liquid cryogen,which enlarges the principles originally set forth in the aforementionedcopending and commonly assigned application.

It is another object of the invention to provide a process for thecooling of an object in housing, e.g. a superconductive magnet in acryostat, a conductive cable system or a superconductive magnet directlytraversed by a cryogen, whereby the aforementioned disadvantages areobviated.

Another object of the invention is to provide an apparatus or system forthe cooling of objects with a liquid cryogen whereby the continuity offlow to the cooled object from a supply vessel can be maintained.

Still another object of the invention is to provide a method of and anapparatus for the continuous supply of a cryogen to, and effectivecooling of, an object to be cooled especially a superconductive systemfor long periods and with a single supply vessel serving as a source ofthe liquid cryogen to the object to be cooled.

SUMMARY OF THE INVENTION These objects and others which will becomeapparent hereinafter are attained, in accordance with the presentinvention, in that the partly vaporized coolant (i.e. the mixture of gasand liquid phases of the cryogen) is passed in heat exchangingrelationship with previously warmed compressed coolant and is fullyevaporated and heated thereby before being compressed anew; thecompressed coolant or cryogen passes after this heat exchange andcooling thereby into the storage vessel into which it is expanded.

This process, according to the present invention, has been found toconstitute a simple and energyconserving solution to the problems ofcontinuously cooling a body with cryogenic liquids.

The cooling of the object according to the present invention is thuseffected with a deep-cooled liquid coolant or cryogen from a storagevessel, preferably after some supcrcooling (i.e. cooling to atemperature below its boiling point) while the heat input from theexterior to the cryostat in which the object is maintained and the heatinput to the connecting ducts between the storage vessel and thecryostat is compensated by the heat pickup by the expanded coolant fromthe object so that a part of the liquid coolant is thereby vaporized. Afurther portion of the vapor phase of the coolant is used for thesupercooling of the cryogen supplied from the storage vessel to theobject.

The sensible'cold and the cooling capacity of the partly expandedcryogen is first transferred to the compressed cryogen by heat exchangeso that the compressed cryogen is cooled and is thereafter expanded intothe storage vessel. All of the aforementioned steps of the presentinvention can be carried out continuously so that periodically effectivepressurizations and depressurizations are avoided and the complexcontrol systems characterizing earlier techniques, can be minimized, oreliminated.

The cold loss of the process is not only compensated by vaporization ofthe liquid coolant stored in the vessel but also by utilization of thegas enthalpy of the vaporized cryogen so that the evaporation rate ofthe liquid coolant is significantly reduced.

The process and apparatus of the present invention is mostadvantageously utilized for the continuous cooling of superconductivesystems as, for example, superconductive magnets, utilizing supercooledliquid helium as the cryogen. From the point of view of advantageouscontrol of the process, the compressed and cooled cryogen is directlyexpanded into the storage vessel to the displacement pressure, i.e. thepressure whereby the cryogen is forced from the storage vessel to thecooled object.

According to a further feature of the invention, radiation shields, egas described in the aforementioned copending application, whichconstitute further heat barriers within the cryostat in which the objectto be cooled is disposed and within the ductwork between the storagevessel and the cryostat, are cooled by a part of the gaseous coolantgenerated in the system and which has a temperature greater than about10K.

Of course, the process may be used for the cooling of a single object orfor the cooling of a plurality of such objects traversed by the coolantin series and/or in parallel.

According to another aspect of the invention, an apparatus for carryingout the process and for cooling an object, such as a superconductivedevice in a cryostat, comprises a storage vessel for the deep-cooledliquid cryogen, feed-duct means for delivering the liquid cryogen fromthe storage vessel to the cryostat, return duct means for carrying theliquid cryogen away from the cryostat or the object to be cooled, athrottle valve permitting partial expansion of the cryogen after it hastraversed the object, a heat exchanger for passing the resultinggas/liquid phase mixture in heat-exchanging relationship with thecompressed cryogen, a compressor to which the fully expanded cryogen issupplied and which delivers the compressed and warmed cryogen to theheat exchanger. The heat exchanger is advantageously coupled with anevaporator having a flow cross section for the compressed cryogen whilethe apparatus may comprise a plurality of heat exchangers connected inseries and to the evaporator. An expansion valve may be disposed at theinlet to the storage vessel.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, featuresand advantages of the present invention will become more readilyapparent from the following description, reference being made to theaccompanying drawing, the sole FIGURE of which is a flow diagramillustrating the invention.

SPECIFIC DESCRIPTION AND EXAMPLES In the drawing, I have shown a systemfor the cooling of a superconductive magnet 6, preferably in a cryostatnot illustrated in detail but of the type described in theaforementioned copending application, with liquid helium. Liquid heliumat a displacement pressure of about 2 bars and a temperature of about 5Kfrom a storage vessel 1 through a heat exchanger 2 in which the liquidhelium is supercooled to a temperature of about 4.6K.

The supercooled liquid helium is passed through the central duct 3 of aconduit system 4 (consisting of coaxially nested ducts as described inthe aforementioned copending application) to the superconductive magnet6 disposed within the cryostat represented by the dotdash line 5. Thesuperconductive magnet 6'and the interior of the cryostat 5 is held bythe cooling process to a constant temperature of about 4.6K.

The liquid cryogen flows from the superconductive magnet 6 through anexpansion valve 8 in which it is expanded against a pressure of 1.2 barsto form a gas/liquid phase mixture traversing the tube coil 9 which mayrepresent a heatshield surrounding the superconductive magnet so as toprevent entry .of external heat into the cooling. zone. A portion of theliquid coolant is transformed to:vapor at the expansion valve 8 and afurther portion is vaporized in the tube coil 9 by pickup of such leakedheat. From the tube coil 9 the gas/liquid phase mixture passes throughthe innermost annular duct 10 of the conduit system 4 and anotherportion is evaporated. in this passage 10, the cryogen mixture acts as aheat shield absorbing heat leaking from the exterior inwardly.

The gas/liquid phase mixture then enters the heat exchanger 2 in whichit is passed in heat-exchanging relationship with the liquid helium fromthe storage vessel 1 to supercool the latter, the heat abstracted by themixture resulting in a further evaporation of liquid in the latterstream. The remainder of the liquid of this stream is evaporated in theevaporator 11 connected to the warm side of the heat exchanger 2 and inthe heat exchangers 13, 14, 15 and 16 connected in series with oneanother and the evaporator 11. The gaseous coolant is then compressed incompressor 17 to a pressure of about 15 bars and is at a temperature of290K.

compressing said fully gaseous fluid to form a compressed fluid andabstracting heat from said compressed fluid by passing same inheat-exchanging relationship with said mixture to supply thereto atleast part of the heat required for the complete vaporization of theliquid phase thereof, thereby "forming a cooled compressed gas; andexpanding said cooled gas into said vessel to supply liquefied fluidthereto. I v

2. The method defined in claim 1 wherein said compressed cooled gasexpanded to said displacement pressure in said vessel. 7

3. The method defined in claim 1, further comprising derivingva warmpartial stream of gas from the mixture during the evaporation thereofand, forming therefrom a heat-absorbingshield for a colder portion ofthe cryo- The compressed helium flows through the heat exchangers 16,l5, 14, 13 in succession and through the evaporator 11 in sectionsseparated from those transverscd by the expanded helium and is cooled toa temperature of about 5.2K.

The fluid is then permitted to expand to a pressure of 2 bars, thedisplacement pressure of the liquid helium, at the throttle valve 18into the storage vessel 1. This expansion reduces the temperature toabout 5K and introduces a mixture of 42% by weight liquid and 58% byweight vapor into the storage vessel 1.

To cool the annular passage 19 serving as a radiation shield, thepassages 20 and 21 of the duct system are evacuated and a portion of thelow pressure helium at a temperature of about llK is drawn off via line23 and fed to the radiation shield 19. This portion of the low pressurehelium can be fed also to the tube coil 22 which may be disposed in anouter radiation shield of the cryostat (see the aforementioned copendingapplication). After heating to a temperature of 100K, this partialstream is returned via line 24 to the compressor 17. A pressurecontroller 25 controls the throttle valve 18 to maintain thedisplacement pressure in the vessel 1.

I claim: 1. A method of cooling an object with a lowtemperaturecryogenic fluid, comprising the steps of:

passing the liquefied fluid at a cryogenic temperature continuously froma storage vessel into heatexchanging relationship with said object andunder a displacement pressure; partly expanding the liquefied fluid toform a gas/liquid phase mixture; fully vaporzing said mixture by heatexchange to form a completely gaseous fluid;

genie fluid.

4. The method defined in claim 1, further comprising the step ofsupercooling the liquefied fluid between said vessel and said object inheat exchange with said mixture.

5. The method defined in claim 4 wherein said liquefied fluid betweensaid vessel and said object is passed through a duct, said methodfurther comprising the step of shielding said duct with a sheath of saidmixture.

6. The method defined in claim 5 wherein said object is enclosed in acryostat provided with a radiation shield, said method furthercomprising the step of cooling said radiation shield with said mixture.

7. The method defined in claim 6, further comprising the step ofderiving a partial gas stream from said mixture during the evaporationthereof and enclosing said duct in a sheath of said partial gas stream.

8. The method defined in claim 7 wherein said cryostat is provided withanother radiation shield outwardly of the first-mentioned radiationshield, said method further comprising the step of cooling said furtherradiation shield with said partial gas stream.

9. An apparatus for cooling an object contained in a cryostat, saidapparatus comprising:

a storage vessel for a liquid cryogen;

a duct connecting said storage vessel with said cryostat for passingsaid liquid cryogen into heatexchanging relationship with said object;

means for leading cryogenic fluid from said object;

heat-exchanger means having a first flow section traversed by saidcryogenic fluid for converting same to a fully gaseous state;

a compressor connected to said heat-exchanger means for compressing thefully gaseous cryogenic fluid and forming a heated compressed fluid,said heat-exchanger means having a second flow crosssection traversed bysaid heated compressed fluid to cool the latter; and

an expansion valve between said second flow crosssection and said vesselfor expanding the compressed fluid cooled in said heat-exchanger meansinto said vessel and liquefying the fluid expanded therein.

10. The apparatus defined in claim 9 wherein said heat-exchanger meansincludes an evaporator and a plurality of heat exchangers connected inseries and to said evaporator, said apparatus further comprising anotherheat exchanger traversed by the fluid derived from said object and theliquid cryogen for passing same in heat-exchanging relationship tosupercool said liquid cryogen and partial evaporate the fluid led fromsaid object.

11. The apparatus defined in claim 10 wherein said means for leadingfluid from said object comprises a duct traversed by the latter fluid,said apparatus further pansion valve for transforming liquid cryogcninto a gas/liquid phase mixture.

15. The apparatus defined in claim 14 wherein said cryostat is formedwith a radiation shield disposed between the exterior and said object,said apparatus further comprising means for cooling said radiationshield with said mixture.

16. The apparatus defined in claim 15 wherein said cryostat furthercomprises another radiation shield outwardly of the first-mentionedradiation shield, and

means for passing said partial stream through said other radiationshield.

17. The apparatus defined in claim 16 wherein said object is asuperconductive magnet.

1. A method of cooling an object with a low-temperature cryogenic fluid,comprising the steps of: passing the liquefied fluid at a cryogenictemperature continuously from a storage vessel into heat-exchangingrelationship with said object and under a displacement pressure; partlyexpanding the liquefied fluid to form a gas/liquid phase mixture; fullyvaporzing said mixture by heat exchange to form a completely gaseousfluid; compressing said fully gaseous fluid to form a compressed fluidand abstracting heat from said compressed fluid by passing same inheat-exchanging relationship with said mixture to supply thereto atleast part of the heat required for the complete vaporization of theliquid phase thereof, thereby forming a cooled compressed gas; andexpanding said cooled gas into said vessel to supply liquefied fluidthereto.
 1. A method of cooling an object with a low-temperaturecryogenic fluid, comprising the steps of: passing the liquefied fluid ata cryogenic temperature continuously from a storage vessel intoheat-exchanging relationship with said object and under a displacementpressure; partly expanding the liquefied fluid to form a gas/liquidphase mixture; fully vaporzing said mixture by heat exchange to form acompletely gaseous fluid; compressing said fully gaseous fluid to form acompressed fluid and abstracting heat from said compressed fluid bypassing same in heat-exchanging relationship with said mixture to supplythereto at least part of the heat required for the complete vaporizationof the liquid phase thereof, thereby forming a cooled compressed gas;and expanding said cooled gas into said vessel to supply liquefied fluidthereto.
 2. The method defined in claim 1 wherein said compressed cooledgas is expanded to said displacement pressure in said vessel.
 3. Themethod defined in claim 1, further comprising deriving a warm partialstream of gas from the mixture during the evaporation thereof andforming therefrom a heat-absorbing shield for a colder portion of thecryogenic fluid.
 4. The method defined in claim 1, further comprisingthe step of supercooling the liquefied fluid between said vessel andsaid object in heat exchange with said mixture.
 5. The method defined inclaim 4 wherein said liquefied fluid between said vessel and said objectis passed through a duct, said method further comprising the step ofshielding said duct with a sheath of said mixture.
 6. The method definedin claim 5 wherein said object is enclosed in a cryostat provided with aradiation shield, said method further comprising the step of coolingsaid radiation shield with said mixture.
 7. The method defined in claim6, further comprising the step of deriving a partial gas stream fromsaid mixture during the evaporation thereof and enclosing said duct in asheath of said partial gas stream.
 8. The method defined in claim 7wherein said cryostat is provided with another radiation shieldoutwardly of the first-mentioned radiation shield, said method furthercomprising the step of cooling said further radiation shield with saidpartial gas stream.
 9. An apparatus for cooling an object contained in acryostat, said apparatus comprising: a storage vessel for a liquidcryogen; a duct connecting said storage vessel with said cryostat forpassing said liquid cryogen into heat-exchanging relationship with saidobject; means for leAding cryogenic fluid from said object;heat-exchanger means having a first flow section traversed by saidcryogenic fluid for converting same to a fully gaseous state; acompressor connected to said heat-exchanger means for compressing thefully gaseous cryogenic fluid and forming a heated compressed fluid,said heat-exchanger means having a second flow cross-section traversedby said heated compressed fluid to cool the latter; and an expansionvalve between said second flow cross-section and said vessel forexpanding the compressed fluid cooled in said heat-exchanger means intosaid vessel and liquefying the fluid expanded therein.
 10. The apparatusdefined in claim 9 wherein said heat-exchanger means includes anevaporator and a plurality of heat exchangers connected in series and tosaid evaporator, said apparatus further comprising another heatexchanger traversed by the fluid derived from said object and the liquidcryogen for passing same in heat-exchanging relationship to supercoolsaid liquid cryogen and partial evaporate the fluid led from saidobject.
 11. The apparatus defined in claim 10 wherein said means forleading fluid from said object comprises a duct traversed by the latterfluid, said apparatus further comprising an annular conduit surroundingsaid duct.
 12. The apparatus defined in claim 11 wherein said means forleading fluid from said object includes said conduit whereby the fluidled from said object forms a sheath around said duct.
 13. The apparatusdefined in claim 11, further comprising means for withdrawing a partialstream of gas from said heat-exchanger means and passing same throughsaid conduit to form a sheath around said duct.
 14. The apparatusdefined in claim 13 wherein said means for leading fluid from saidobject includes an expansion valve for transforming liquid cryogen intoa gas/liquid phase mixture.
 15. The apparatus defined in claim 14wherein said cryostat is formed with a radiation shield disposed betweenthe exterior and said object, said apparatus further comprising meansfor cooling said radiation shield with said mixture.
 16. The apparatusdefined in claim 15 wherein said cryostat further comprises anotherradiation shield outwardly of the first-mentioned radiation shield, andmeans for passing said partial stream through said other radiationshield.